A198686 4*7^n-1.

3, 27, 195, 1371, 9603, 67227, 470595, 3294171, 23059203, 161414427, 1129900995, 7909306971, 55365148803, 387556041627, 2712892291395, 18990246039771, 132931722278403, 930522055948827, 6513654391641795, 45595580741492571

Offset: 0

Author

Vincenzo Librandi, Oct 29 2011

Keywords

• nonn
• easy

Links

• Vincenzo Librandi, Table of n, a(n) for n = 0..1000
• Index entries for linear recurrences with constant coefficients, signature (8,-7).

Crossrefs

Cf. A048473, A081655, A198480, A198647.

Programs

Magma

[4*7^n-1: n in [0..30]]

Mathematica

4*7^Range[0,20]-1 (* or *) LinearRecurrence[{8,-7},{3,27},20] (* Harvey P. Dale, Dec 27 2011 *)

Formula

a(n) = 7*a(n-1)+6. a(n) = 8*a(n-1)-7*a(n-2), n>1.

G.f. ( 3+3*x ) / ( (7*x-1)*(x-1) ). - R. J. Mathar, Oct 30 2011